Modified Density Gradient Theory for Surfactant Molecules Applied to Oil/Water Interfaces

Prediction of Micellar Thermodynamics of Nonionic Surfactants Based on the Square Gradient Theory

A geometry-dependent contribution based on the square gradient theory of van der Waals is proposed as a predictive modification of the interfacial energy contribution for the micellar thermodynamic theory. The model has an analytic prediction for the spherical and cylindrical geometries. For ellipsoidal geometry, a simple yet physically meaningful approximation is proposed. The critical micelle concentration (CMC) and the surface tension isotherm under the new contribution are compared with the classical theory. The modified model describes qualitatively the available experimental data and the surface isotherm, showing an improvement in the predictions of the CMC.

Chemical computational approaches for optimization of effective surfactants in enhanced oil recovery

The surfactant flooding becomes an attractive method among several Enhanced Oil Recovery (EOR) processes to improve the recovery of residual oil left behind in the reservoir after secondary oil recovery process. The designing of a new effective surfactant is a comparatively complex and often time consuming process as well as cost-effective due to its dependency on the crude oil and reservoir properties. An alternative chemical computational approach is focused in this article to optimize the performance of effective surfactant system for EOR. The molecular dynamics (MD), dissipative particle dynamics (DPD) and density functional theory (DFT) simulations are mostly used chemical computational approaches to study the behaviour in multiple phase systems like surfactant/oil/brine. This article highlighted a review on the impact of surfactant head group structure on oil/water interfacial property like interfacial tensions, interface formation energy, interfacial thickness by MD simulation. The effect of entropy in micelle formation has also discussed through MD simulation. The polarity, dipole moment, charge distribution and molecular structure optimization have been illustrated by DFT. A relatively new coarse-grained method, DPD is also emphasized the phase behaviour of surfactant/oil/brine as well as polymer-surfactant complex system.

Bulk and Interfacial Properties of the Decane + Water System in the Presence of Methane, Carbon Dioxide, and Their Mixture

Molecular dynamics simulations are carried out to study the two-phase behavior of the n-decane + water system in the presence of methane, carbon dioxide, and their mixture under reservoir conditions. The simulation studies were complemented by theoretical modeling using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) and density gradient theory. Our results show that the presence of methane and carbon dioxide decreases the interfacial tension (IFT) of the decane + water system. In general, the IFT increases with increasing pressure and decreasing temperature for the methane + decane + water and carbon dioxide + decane + water systems, similar to what has been found for the corresponding decane + water system. The most important finding of this study is that the presence of carbon dioxide decreases the IFT of the methane + decane + water system. The atomic density profiles provide evidence of the local accumulation of methane and carbon dioxide at the interface, in most of the studied systems. The results of this study show the preferential dissolution in the water-rich phase and enrichment at the interface for carbon dioxide in the methane + carbon dioxide + decane + water system. This indicates the preferential interaction of water with carbon dioxide relative to methane and decane. Notably, there is an enrichment of the interface by decane at high mole fractions of methane in the methane/decane-rich or methane/carbon dioxide/decane-rich phase. Overall, the solubility of methane and carbon dioxide in the water-rich phase increases with increasing pressure and temperature. Additionally, we find that the overall performance of the PC-SAFT EoS and the cubic-plus-association EoS is similar with respect to the calculation of bulk and interfacial properties of these systems.

Thermodynamics, Microstructures, and Solubilization of Block Copolymer Micelles by Density Functional Theory

Block copolymer micelle is one of the most versatile self-assembled structures with applications in drug delivery, cosmetic products, and micellar-enhanced ultrafiltration. The key to design an effective block copolymer to form micelles is to understand how molecular architecture affects critical micelle concentrations, micellar dimensions, and partitioning of solute into the micelle. In this work, we studied micelles from nonionic block copolymers using interfacial statistical associating fluid theory a density functional theory, which explicitly includes block copolymer-water hydrogen bonding and water-water hydrogen bonding. We are able to predict and explain how micellar thermodynamic properties depend on polymer chain architecture. Dimension and aggregation of micelles are investigated for block copolymers with different hyrophobes and hydrophiles. The effects of temperature and pressure on micelle stability are also captured by the theory. The enhanced solubility of hydrophobic substance in water by micelle loading is demonstrated, and predicted solute distribution answers the question about the locus of benzene in micelles from a theoretical perspective.

Density functional approach to the description of the structure of dimer nanoparticles at liquid–liquid interfaces

A density functional approach to the description of the structure of dimer nanoparticles at liquid–liquid interfaces.